(Reuters) - Afghanistan needs urgent and sustained support from the international community to prevent a larger humanitarian crisis, the head of the U.N. refugee agency said, warning of global implications if that were to happen.

       "The humanitarian situation in Afghanistan remains desperate," U.N. High Commissioner for Refugees Filippo Grandi said in a statement after a three-day visit to the South Asian nation.

       "If public services and the economy collapse, we will see even greater suffering, instability, and displacement both within and outside the country," he added in Wednesday's statement.

       "The international community must therefore engage with Afghanistan – and quickly – in order to prevent a much bigger humanitarian crisis that will have not only regional, but global implications."

       Even before the Taliban took over last month, Grandi said, more than 18 million Afghans, or about half the population, required humanitarian aid.

       More than 3.5 million Afghans were already displaced in a country that is battling drought and the COVID-19 pandemic.

       Poverty and hunger have spiralled since the Taliban takeover, and U.N. Secretary-General Antonio Guterres told an international aid conference this week that Afghans are facing "perhaps their most perilous hour".

       Donors at the conference pledged more than $1.1 billion to help Afghanistan.

       (Writing by Raju Gopalakrishnan; Editing by Clarence Fernandez)